At the end of World War One, Kaiser Wilhelm II abdicated and fled to Holland. The new Government which replaced him initially met in Weimar as there were security risks in Berlin. So, it became known as the Weimar Republic.
Parliament was elected through a system of proportional representation, in which German citizens would vote for a party rather than a candidate.
This resulted in the election of many small parties. No one party could gain a majority and the country was run by coalitions (majorities brought about by different parties working together). This led to disagreements between parties and a lack of decisive action.
The Weimar Constitution had serious consequences for the Weimar Government. Its survival relied on small parties cooperating with each other. Moreover, dictatorship was a real possibility.